THE NEMATODE FAMILY GI^ATHOSTOMID.Ej 247 



Family Diagnosis. 



GxATHOSTOMiD.E Railliet, 1895. 



Spirm'oidea*!?): with two large, trilobed, lateral li]3S, having 

 the cuticle of their iiiuer surfaces thickened and usually raised 

 into longitudinal tooth-like ridges which meet or interlock with 

 those of the other lip. Tail of male with more or less well- 

 developed lateral alye and two spicules. The vagina runs forward 

 from the vulva before giving off the two or four uterine 

 branches. Eggs with thin shells, ornamented externally with 

 fine granulations. 



Key to Subfamilies of Gnathostomidae. 



A. Cuticle behind the lips distended into a head-bulb 



by four submedian ballonets, a process from each 

 of which extends into the bodj'-cavity beside the 

 oesophagns as a cervical sac Gnathostomince (p. 254). , 



B. Head-bulb, ballonets, and cervical sacs absent Spiroxyina. 



SPIROXYIN.^, subfam. n.f 



These Gnathostomidas are without head-bulb, cervical sacs, or 

 ballonets. Their lips are characteristic. A deep cleft parts from 

 the body the whole thickness of the dorsal and ventral edges of 

 each, while the pulp of the middle lobe is separated from the 

 pulps of the adjacent lobes by indentations so deep as to produce 

 an appearance wdiich has been aptly likened by Schneider (1866, 

 p. 125) to the club on a playing-card (PL I. fig. 2, PI. II. fig. 7). 

 Each lobe carries a papilla, the subdorsal and subventral papillae 

 having conspicuous and the lateral papillae inconspicuous termin- 

 ations. The cuticle supporting the inner surfa,ce of each middle 

 lobe is greatly thickened, and pi-ojects anteriorly beyond the edge 

 of the lip as a sharp tooth-like prominence. 



The cuticle of the tail in the male is expanded laterally into 

 alae and ventrally into vesicular swellings, which recall the 

 ventral fusion of the alae in Physaloptera. There ai'e eleven pairs 

 of caudal papillae J, of which two pairs are definitely ventral, one 

 pair lying in front of, the other behind, the cloacal opening ; the 

 other nine are more lateral. Of these lateral papillae Nos. 2 

 and 5 are situated more ventrally than the others ; six are post- 

 anal and three preanal, atid in general the distension of the 



* Hall (1916) makes Railliet's superfamily Spiruvoidea a synonym of Orley's 

 family Spiruridre, of the superfamily Pilarioidea. If this system of classification is 

 followed, there is no group of higher than family rank, embracing nematodes with 

 paired lateral lips, to which the present family can be assigned. We therefore use 

 the name of the superfamily Spiruroidea in this siense. 



+ For subfamily diagnosis, see p. 248. 



X Note, — Throughout our descriptions and in our figures we have numbered 

 the caudal papillfs of the male worms consecutively' from the extremity of the tail 

 forwards — the first pair, or " No. 1," being that nearest to the tip. 



